Unfinished base in Fenland city in a bad way? (6)
I believe the answer is:
evilly
'in a bad way?' is the definition.
(I've seen this in another clue)
'unfinished base in fenland city' is the wordplay.
'unfinished' means to remove the last letter.
'base' becomes 'vile' (synonyms).
'in' means one lot of letters goes inside another.
'fenland city' becomes 'ely' (Ely is a city in the Fens).
'vile' with its last letter removed is 'vil'.
'vil' put inside 'ely' is 'EVILLY'.
(Other definitions for evilly that I've seen before include "In wicked or depraved way" , "With wicked intent" , "Extremely wickedly" , "In a very wicked manner" , "in a bad way" .)